Is an Adjustable Rate Mortgage (ARM) Right for You?

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An adjustable rate mortgage, called an ARM for short, is a mortgage with an interest rate that is linked to an economic index. The interest rate and your payments are periodically adjusted up or down as the index changes.

ARM Terminology

  • Index: A mortgage index is a guide that lenders use to measure interest rate changes. Common indexes used by lenders include the activity of one-, three-, and five-year Treasury securities, but there are many others. Each ARM is linked to a specific index.
  • Margin: Think of the margin as the lender's markup. It is an interest rate that represents the lender's cost of doing business plus the profit they will make on the loan. The ARM margin is added to the index rate to determine your total interest rate. It usually stays the same during the life of your home loan.
  • Adjustment Period: The adjustment period is the period between potential interest rate adjustments. The date on which the interest rate changes is known as the mortgage reset date,

You may see an ARM described with figures such as 3/1 or 5/1. The first figure in each set refers to the initial period of the loan, during which your interest rate will stay the same as it was on the day you signed your loan papers.

The second number is the adjustment period, showing how often adjustments can be made to the rate after the initial period has ended. The examples above are all ARMs with annual adjustments — meaning adjustments could happen every year.

The chart below illustrates 5/1-year ARM average from the year 2005 through 2019.

If My Payments Can Go Up, Why Should I Consider an ARM?

The initial interest rate for an ARM is lower than that of a fixed-rate mortgage, where the interest rate remains the same during the life of the loan. A lower rate means lower payments, which might help you qualify for a larger loan.

How long do you plan to own the house? The possibility of rate increases isn't as much of a factor if you plan to sell the home within a few years.

Do you expect your income to increase? If so, the extra funds might cover the higher payments that result from rate increases.

Some ARMs can be converted to a fixed-rate mortgage. However, conversion fees could be high enough to take away all of the savings you saw with the initial lower rate.

ARM Indexes

While you can't dictate which index a lender uses, you can choose a loan and lender based on the index that will apply to the loan. Ask the lender how each index used has performed in the past. Your goal is to find an ARM that is linked to an index that has remained fairly stable over many years.

When comparing lenders, consider both the index and the margin rate being offered.

Discounted Rates and Buydowns

When you're buying a home you might encounter sellers who offer to pay a buy-down fee that allows the lender to offer you an initial rate that's lower than the sum of the index and the margin. New home builders sometimes offer that type of purchase package to help get people into their homes.

The buy-down rate will eventually expire and your payments could rise significantly if an ARM rate is adjusted upwards at the same time the discount expires.

Keep in mind that sellers sometimes raise the price of a home by the amount they pay to buy-down your loan. The extra cost may in time override any savings from the initial discount.

Interest Rate Caps

Rate caps limit how much interest you can be charged. There are two types of interest rate caps associated with ARMs.

  • Periodic caps limit the amount your interest rate can increase from one adjustment period to the next. Not all ARMs have periodic rate caps.
  • Overall caps limit how much the interest rate can increase over the life of the loan. These are also called "lifetime caps." Overall caps are required by law.

Payment Caps

A payment cap limits how much your monthly payment can increase at each adjustment. ARMs with payment caps often do not have periodic rate caps.

Carryovers

If an interest rate cap held your interest down at an adjustment even though the index went up, the amount of the increase can be carried over to the next adjustment period.

Beware of Negative Amortization

Amortization takes place when payments are large enough to pay the interest due plus a portion of the principal.

Negative amortization occurs when payments do not cover the cost of interest. The unpaid amount is added back to the loan, where it generates even more interest debt. If this continues, you could make many payments, but still owe more than you did at the beginning of the loan.

Negative amortization generally occurs when a loan has a payment cap that keeps monthly payments from covering the cost of interest.

Lenders are required to give you written information to help you compare and select a mortgage. Don't hesitate to ask as many questions as it takes to help you understand every aspect of ARMs and other home loans that are offered to you.

Get the Facts About Adjustable Rate Mortgages

What are the risks of an adjustable rate mortgage? To reduce your risks, consider the following issues before accepting an ARM.

Discounted Rates - Buydowns
Sellers sometimes pay a fee that allows the lender to offer you an initial rate that's lower than the sum of the index and the margin. The buy-down rate will eventually expire.

  • The Double Whammy
    Your payments can rise significantly if your rate is adjusted upwards at the same time the discount expires.
  • Is a Discounted Rate Worthwhile? Sellers may raise the price of a home by the amount they pay to buy-down your loan. The extra cost may in time override any savings from the initial discount.

Interest Rate Caps
Rate caps limit how much interest you can be charged. There are two types of interest rate caps associated with ARMs.

  • Periodic caps limit the amount your interest rate can increase from one adjustment period to the next. Not all ARMs have periodic rate caps.
  • Overall caps limit how much the interest rate can increase over the life of the loan. Overall caps are required by law.

Payment Caps
A payment cap limits how much your monthly payment can increase at each adjustment. ARMs with payment caps often do not have periodic rate caps. 

Carryovers
If an interest rate cap has held your interest down even though the index went up, the amount of the increase can be carried over to the next adjustment period.

Negative Amortization
Amortization takes place when payments are large enough to pay the interest due plus a portion of the principle.

  • Negative amortization occurs when payments do not cover the cost of interest. The unpaid amount is added back to the loan, where it generates even more interest debt. If this continues, you could make many payments, but still owe more than you did at the beginning of the loan.
  • Negative amortization generally occurs when a loan has a payment cap that keeps monthly payments from covering the cost of interest.
  • Negative amortization does not have as much of an impact when real estate is appreciating nicely, so the lower payments may be more attractive to you than paying down the principle.

Lenders are required to give you written information to help you compare and select a mortgage. Don't hesitate to ask as many questions as it takes to help you understand every aspect of your loan.

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Sources
The Balance uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. The Federal Reserve Board. "Consumer Handbook on Adjustable-Rate Mortgages," Page 15.

  2. The Federal Reserve Board. "Consumer Handbook on Adjustable-Rate Mortgages," Page 10.

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